Gas-blast circuit interrupter with insulating arc shield

ABSTRACT

A gas-blast circuit interrupter has a pair of separable contacts, at least one of which is movable, and a stationary insulating arc shield is disposed immediately adjacent the contacts, and encompasses a critical portion of the initial travel of the cooperable movable contact, so that the space vacated by the movable contact, during initial opening travel, does not communicate with the pressurized space, which contains the interrupting gas to be used later in the interruption of the established arc. Following withdrawal of the movable contact from the insulating arc shield, of at least one inch in length, it is exposed to a radially inward flow of cool gas supplied by suitable piston means, or another high-pressure source, if desired.

United States Patent [191 Milianowicz GAS-BLAST CIRCUIT INTERRUPTERINSULATING ARC SHIELD m1 3,814,883 1 June 4, 1974 3,291,948 l2/l966Telford 200/148 A 3.555.225 l/l97l Saffold et al 200/148 A [75] mentor:a lgflianowicz Primary Eraminer-Robert S. Macon onmev' Attorney, Agent,or Firm-W. R. Crout [73] Assignee: Westinghouse Electric Corporation,

- Pittsburgh, Pa. I [57] ABSTRACT [22] Filed: Nov. 3, 1972 A gas-blastcircuit interrupter has a pair of separable contacts, at least one ofwhich is movable, and a stal PP 303,579 tionary insulating arc shield isdisposed immediately Related [1.8. Application Data adjacent thecontacts, and encompasses a critical por- [63] Cominuammimpart of L709July I tion of the initial travel of the cooperable movable 1970'abandone I contact, so that the space vacated by the movable a qcontact,during initial opening travel, does not com- 52 US. Cl. 200/148 G,200/150 G munieate with the Pressurized Spaee, which eentains 511 int.cl. H0lh 33/70 the interrupting gas to be used later in the interruption5 Field f Search 200 148 3 1506 143 R of the established arc. Followingwithdrawal of the movable contact from the insulating arc shield, of at5 References Cited least one inch in length, it is exposed to a radiallyin- UNITED STATES- PAT'ENTS ard flow of cool gas supplied by suitablepiston v v means, or another high-pressure source, if desired. 2,442,0105/1948 Leeds et al. 200/150 G. 3,095,490 6/1963 Cromer et al.....200/148 A 10 Claims, 6 Drawing Figures Q J2 L I6!) :1

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mum a PATENTEBJIIR 41w INVENTOR I WITNESSES I 1 GAS-BLAST CIRCUITINTERRUPTER WITH INSULATING ARC SIIIELD CROSS-REFERENCES TO RELATEDAPPLICATIONS v This patent application is a continuation-in-part of mypatent application filed July 1, 1970, Ser. No.

51,709 and now abandoned.

. BACKGROUND OF THE INVENTION lt is an established-fact that in order tointerrupt large short-circuit currents at a significant value oftransient recovery voltage, there must be a gap of considerable lengthbetween the arcing electrodes. The interruption of power arcs does notreadily take place with very short electrode separations. The removal ofarc prod ucts from the vicinity of the arcing electrodes by providing aflow of cool gas through the arcing region is at present the majorrequirement in a successful type of fluid-flow circuit interrupter.

The contamination of the arc chamber with the are products during thetime when the contact separation is insufficient to attemptinterruption, has been accepted, heretofore, as a natural consequence ofthe fact that the contacts separate, and take time to move apart to adistancel'where the interruption can occur.

Indeed, U.S. Pat. No. 2,442,010 by Winthrop M. Leeds and Benjamin P.Baker, describes an interrupter, which requires a plurality ofaxially-disposed chambers separated by insulating plates, which arerequired to effect a current interruptionjFlG. 2 in US. Pat. No.2,442,010 shows clearly that the arc, and consequently the'arc products,have free access to the interrupting fluid for about 50 percent of themovable contact travel after the contacts separate. ln contrast to this,with reference to the interrupter described in my invention, areproducts have access to the interrupting gas for a distance of only 12.5percent of movable contact travel after contact separation, thisconstruction being accomplished by only one arc shield.

Reference also may be had to 1.1.5. Patent Applicationiiled July 31,1967, Ser. No. 657,122 by Russell E. Frink and Stanislaw A. Milianowicz,entitled Delayed- Blast Fluid-Flow Circuit lnterrupter, and assigned tothe assignee of the instant application, for a general description of afluid-flow circuit interrupter in which puffer means is utilized tosupply a blast of gas, such as sulfur hexafl uoride (SP6) gas, toward anestablished arc to effect the latters extinction. Additional referencemay be made to US. patent application filed Sept. 25, 1967 Ser. No.670,168 by Thomas F. Saffold and Russell E. Frink entitled Fluid-FlowCircuit lnterrupter with Arc-Assisted Piston Action, and similarlyassigned to the same assignee, for a further description of an SFfluid-flow type of circuit interrupter.

SUMMARY OF THE INVENTION In accordance with a preferred embodiment ofthe present invention, there is supplied a pair of separable cooperablecontacts, both of which must be vented into the general gas enclosure.An insulating arcing shield encompasses a portion of the stationarycontact structure, and extends axially at least one inch in thedirection of opening travel of the movable contact, so that for at leastone inch of initial arcing distance, the are products are not allowed toenter the fluid-forcing chamber, which contains clean and cool gas. Thisis very important andhas been proven by trying shorter lengths of thearcing shield. For example using a one half inch long arcing shield, theinterrupter could interrupt only about half the valve of current, ascompared with the l-Vs inches long arcing shield which was used in theexperiment, which latter dimension I prefer. However, I believe thatthis performance is not a discontinuous function, and that a fair degreeof improvement can be obtained with a shield which is one inch long.Consequently, the shield should be at least one inch in length. Duringthis initial opening travel of the movable contact, fluid-flow means,such as puffer means are operable, being mechanically connected, forexample, to the movable contact, so as to cause a compression of anarc-extinguishing gas, which is injected laterally inwardly into the arccolumn only following the withdrawal of the movable arcing contact outof the confines of the encompassing insulating arc shield.

It will be noticed that when the movable contact is within the confinesof the arcing shield there is no communication between the gas in thevicinity of the arc and any part 'of gas within the arc-chamber andpiston cylinder system, except that which occurs from clearances betweenparts resulting from required tolerances. At this stage of thecurrent-interrupting operation, the arc products must be vented to thegeneral gas enclosure unlike the interrupter described in the US. Pat.No. 2,442,010 by W. M. Leeds and B. P. Baker, where the are products arepartly injected into their arc control device in order to assist theinterrupting of the current.

This injection of cool gas laterally inwardly into the arc, after it hasattained an initial length, causes rapid are interruption.

It should be stated that another important feature of my improvedcircuit interrupter is the effect of the axial length of the arc shieldon the amount of precompression of the gas in the piston-cylinder systemwhere this method of gas-forcing means is used. Using a 1% inches longare shield, and SP gas in the interrupter housing at 7 5 PSIG ambientpressure, a pressure differential of PSI is produced between the coolgas in the piston-cylinder space and the general gas enclosure, beforethe cool gas is allowed to enter the arc region. Further to theimportance of the value of the pressure differential, it was establishedby means of many experimental trails that the venting areas, and theratio of piston area to the total venting area, were criticallyimportant.

The total venting area for both contacts, which allows for the highperformance of this interrupter, lies between the limits of 1.4 sq. in.to 1.7 sq. in. and the ratio of piston area of the total venting area iscontained in the range of numbers between 9 and 12. The preferred pistonarea was, for example, 15.7 sq. inches when a piston is used.

. 3 My preferred limits for the length of the shielding nozzle is fromone to two inches, and my preferred range of nozzle length is from 1%;to 1-% inches.

To date, the interrupter described in this patent ap plication, and usedin a three-pole circuit breaker on a three-phase circuit hassuccessfully completed current interrupting tests to the AmericanNational Standards Institute requirements for 63,000 amperes at 15 KVrating. This fact permits the capability to build 15 KV, 1,500.MVAswitchgear equipment in a standard 36 inch switchgear cubicle, usingcircuit breakers with no exhaust of any kind. There is none suchavailable in the entire world,- to my knowledge.

To date, a transient recovery voltage of 1,100 volts per microsecond hasbeen obtained at 63,000 amperes interruption, and a current of 89,000amperes has been successfully interrupted.

The above results show that a major breakthrough in the art of power areinterruption has occurred.

Indeed, it is the unprecedented high levelperformance of thisinterrupter that supports the claim to the novelty of this invention,and prior to this no other device, however superficially similar, couldproduce such a high performance.

Those skilled in the art may also recognize the fact that the highperformance of this interrupter may be due not to any single feature-ofthis invention, but to the combination of many features describedherein.

Further objects and'advantages will readily become apparent upon readingthe following specification taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 5 illustrates the fully-opencircuit position of the I movable contact structure; and,

FIG. 6 is a sectional view taken substantially along the line VI-VI ofFIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, andmore particularly to FIG. 1 thereof, the reference numeral 1 generallydesignates a three-pole fluid-blast circuitinterrupter comprising threespaced pole assemblies A, B and C. As will be apparent from FIG. 1, eachpole assembly includes, generally, an upper end plate 2, a generallyupstanding cylindrical housing 3, and a lower end plate and mechanismhousing 4. Disposed exteriorly of the mechanism housing 4 is adrive-crank 5 affixed to an operating shaft 6, and a generallyhorizontally reciprocally movable insulating operating rod 7 ispivotally secured to the external operating crank 5, as at 8, and isconnected to a drive crank 9 through a pivotal connection 10. The threedrive cranks 9, only one of which is shown, are affixed and rotatablewith an operating drive shaft 11, which is connected to a suitablemechanism 12, which constitutes no part of the present invention, andmay be of the type set forth in U.S. Pat. No.

3,183,332 issued May 1 l, 1965 to Russell E. Frink and Paul Olsson, andassigned to the assignee of the present invention.

It will be apparent from FIG. I that a suitable supporting groundedframework 14 is utilized comprising vertical channel members 15 withinterbracing structural steel members 16, having horizontally extendinginsulating support straps 16b secured thereto, which assist insupporting the'interrupting assemblies. Additionally, lower insulatorsupports 17 may be employed extending generally horizontally from achannel support member 160, the latter being affixed to the verticalsupport channels 15.

FIGS. 2 and 3 more clearly illustrate the internal construction of eachof the interrupting assemblies. With reference to FIG. 2, it will benoted that there is provided the cylindrical housing 3 of a suitableinsulating material having at one end thereof the end closure plate 2having a line terminal connection 20 constituting an integral partthereof. At the opposite end of the tubular housing 3 is the operatingcasting 4, within which extends the rotatable operating shaft 6 havingaffixed thereto, as by a key pin 18, an internallydisposed operatingcrank 19, the latter being pivotally connected, as at 20, to a pair ofmetallic operating links 21. The upper ends of the operating links 21,as viewed in FIGS. 2, 3 and 5, are pivotally connected to a pivot pin22, the latter extending through apertures 23 provided in a spider-likeactuator 24, which is fastened, to the end 26a of a movable operatingcylinder 26 having a closed end plate portion 26b.

It will be observed that an insulating arc shield 28 has anaxially-extending flange portion 28a, which is interposed within'acup-shaped stationary contact housing 30, which is elongated, as at 30a,to provide a guiding support for the movable cylinder end plate 26b ofthe puffer assembly, generally designated by the reference numeral 32.Items 30 and 30b, comprise the stationary piston which is supported bytubular guide 30a. Item 30c is a multiple opening in piston 30/30b whichadmits gas to the insulating arc chamber 42. Preferably, the shield 28extends for 1% inches axially from the stationary contact.

Thus, during the opening operation of the interrupter, the operatinglinkage 21, pivotally connected to the movable puffer assembly 32,causes downward gascompressing motion of the movable cylinder end plate26b over the tubular guide support 30a, and causes gas to flow in adirection indicated by the arrows 33 into the insulating stationary arcchamber 34.

It will be observed that the movable contact 35 is vented, having a ventopening 35a therethrough, and cooperates with a plurality of flexiblestationary contact fingers 36, which constitutes generally a slottedtubular member 36a inserted into the cylinder guide support 30a.

Thus, during the initial portion of the opening operation, theinitially-established are 37 is confined by the corrugated insulatingarc shield 28 for at least l-Vs inches in the test interrupterconsidered, and is protected from the lateral blasting effect ofrelatively cool gas caused by compressing motion of the movable pistonring 261), in the test interrupter, thus causing less energy to bereleased at the arc than if it had not been so protected by the shield.I

However, when the movable tubular vented contact 35 has approached theposition indicated in FIG. 4, it

Preferably, asliding ball contact assembly 40 maintains electricalcontact with the movable tubular contact 35, and transfers the currenttherefrom to the lower terminal plate 4a, which is connected with thelower line terminal L2 of the interrupting device.

US. Pat. No. 3,301,986 issued Jan. 31, 1967 to Russell E. Frink andassigned to the assignee of the instant application, generally describesand claims such a balltype sliding contact structure.

- The present invention is not only applicable to sulfurhexafluoride (SFgas-type circuit breakers, either of the puffer-type, as illustratedherein, or of the dualpressure type, as illustrated in US. Pat. No.3,057,983, but also it can be applied to any other gas-flow type ofcircuit interrupter, such as an air-blast type of circuit breaker. Theinvention functions to increase the interrupting capability of theinterrupter by preventing the dissipation of the interrupting qualitiesof the entering gas stream by a confinement'of the hot arc gases duringthe initial arc-lengthening operation. The invention generally utilizesthe arc shield 28', which contains the electrical arc 37 for at leastone inch distance along the moving contact path immediately followingthe contact-part vicinity. The are shield 28 is preferably made ofarc-resistant insulating material, such as polytetrafluoroethylene,commonly sold under the trade name Teflon" by the E. I. Dupont Company.

It is establishedfact that in order to interrupt shortcircuit currentsat a significant value of transient recovery voltage, that there must bea gap of considerable distance between the arcing electrodes. Thisinvention in a test interrupter as described heretofore used 1- /8inches as this dimension for the gap distance between the arcingelectrodes in this particular test interrupter.

The removal of arc products from the vicinity of the arcing electrodes35, 36 by providing a flow of cool gas through the arcing region is atpresent the major requirement in a successful type of fluid-flow circuitinterrupter.

The contamination of the arc chamber 42 with the are products during thetime when the contact separation is insufficient to attempt theinterruption, has been accepted heretofore as a natural consequence ofthe fact that-the contacts separate, and take time to move apart to adistance where the interruption can occur. In order not to contaminatethe arc chamber 42 with are products during the time when nointerruption is possible, the arc shield 28, as used in the presentinvention, is employed to contain the arc37, thereby allowing the areproducts to go to the ambient gas enclosure 39, 43 but preventing themfrom entering the arc chamber 42. When the moving contact 35 does emergefrom the arc shield 28, as shown in FIG. 3, the distance between thecontacts 35, 36 is sufficient to allow interruptionto occur, and the gasin the arc chamber 42 is clean, which it would not be, had there been noarc shield 28, or had the arc shield been made of insufficient length.

The presence of the arc shield 28 increases the capability of aninterrupter considerably. Experimental tests of the first prototype ofthe disclosed gas-blast circuit interrupter have shown that for a 13.2KV device, the fault current interrupted as 70,000 amperes at atransient recovery voltage of 650 volts per microsecond. This value wasreached in a series of 10 KA steps.

' There were no failures, and the maximum performance of thisinterrupter is yet to be established. .With a par ticular device undertests, it was only 6 inches in inside diameter, and 30 inches long, andonly required 250 foot pounds per operation. As a result, it will berealized that a major step in the art of power circuit interruption bygas flow has been taken by the use of the arc shield 28 of the presentinvention of a critical minimum length. Examination of the test resultsindicated that the arc column 37 itself was being considerablyinfluenced.

' During the closing operation of the device, the rotation of theoperating crank 19 causes, through the linkage 21, closing inward travelof the movable tubular vented contact 35 through the arcing chamber 42and into the confines of the corrugated arc shield 28, and intoengagement with the flexible stationary contact fingers 36. FIG. 2represents the device in the closedcircuit position in which the currentpasses therethrough from the terminal plate 2a, through the tubularguide 30a, stationary contact fingers 36, movable tubular vented contact35, roller sliding contact assembly 40, stationary conducting post 45 tothe lower crank housing 4 and to the line terminal L2.

From the foregoing description it will be apparent there there has beenillustrated and described an im-, proved gas-blast circuit interrupter,in which remarkable interrupting performance has been achieved by theuse of an insulating arcing shield 28, which confines at least one inchof the initial travel after contact separation of the movable tubularvented contact 35. As a result, cool inward gas flow is provided,uninfluenced by the hot gases generated within the initial arcing region47.

In the preferred execution of my invention I incorporate a stationaryand movable venting contact member. However, as will be apparent to oneskilled in the art, performance of the device will not be altered if thesta tionary contact is made to move, and the moving contact is heldstationary; or furthermore, if both contacts are made to move. The onlyrequirement in this respect is relative motion of the two contacts.Also, in FIG. 5, which shows the interrupterin the open position,contact 35 is still in contact with the nozzle 34. However, in somecases it may be desirable to slightly increase the relative travel ofthe contacts so that in the fully open position the contact 35 isrelatively completely withdrawn from the nozzle 34.

Although there has been illustrated and described a specific structure,it is to be clearly understood that the same was merely for the purposeof illustration, and that changes and modifications may readily be madetherein by those skilled in the art, without departing from the spiritand scope of the invention.

I claim as my invention:

1. A gas-blast circuit interrupter including, in combination:

a. separable cooperable tubular venting contacts at least one of whichis movable,

b. nozzle-like interrupting structure comprising a relatively stationaryannular imperforate arc shield (28) extending at least one inch alongthe line of movement of said one movable venting contact;

; operating means operable to withdraw the movable venting contact outof said imperforate arc shield (28);

d. said annular arc shield (28) encompassing a minimum portion of atleast one inch of the initial arcing travel of said one movable tubularventing contact. thereby forcing the drawn arc to assume a minimumlength of at least one inch prior to the injection thereto of gas; and,

e. fluid-flow producing means to inject relatively cool I fluid underpressure laterally into the arc stream after said one movable ventingcontact has withdrawn from the imperforate arc shield (28),

2. The gas-blast circuit interrupter of claim 1, wherein the innersurface of the stationary imperforate arc shield 28) is corrugated.

3. The combination according to claim 1, wherein means defines anouterannular second insulating nozzle member (34) spaced outwardly fromsaid inner first nozzle member to thereby define an interveningsubstantially annular inlet passage permitting gas to flow radiallyinwardly at a fixed level at times toward the arc.

g 4. The gas-blast circuit interrupter of claim l,

wherein piston means provides the gas flow.

5. A gas-blast circuit interrupter including a pair of cooperabletubular venting contacts at least one of which is movable, nozzle-likeinterrupting structure comprising a relatively stationary first annularimperforate are shield (28) extending at least one inch along the lineof movement of the movable venting contact, means defining an outerannular second insulating nozzle member (34) spaced outwardly from saidinner first nozzle member to thereby define an intervening substantiallyannular inlet passage permitting gas to flow radially inwardly at afixed level at all times toward the arc, said annular first arc shield(28) encompassing said minimum portion of at least one inch of theinitial arcing travel of the movable tubular venting contact, therebyforcing the drawn arc to assume a minimum length of at least one inchprior to the injection thereto of gas through said inlet passage,whereby to confine the hot arc gases of the initially-drawn portion ofthe established arc of at least 1 inch while simulataneously permittinga venting therefrom through both of said tubular ventingseparablecontacts, operating means to withdraw the movable tubular ventingcontact out of said relatively'stationary first are shield (28) therebyopening up said inlet passage, and gas-flow-producing means for forcingrelatively cool gas under pressure laterally into the arc stream throughsaid relatively stationary inlet passage at said fixed level after themovable tubular venting contact has withdrawn from the first arcingshield (28) and the movable tubular venting contact movable along saidare passage formed in the second nozzle member with relatively slightclearance so that the major proportion of the gas flow directed throughthe arc passage in the-direction of opening movement of the movablecontact passes interiorly of the movable tubular venting contact forventing and arc-extinguishing purposes, and said movable tubular ventingcontact pulling free of said relatively stationary inlet passage andretracting away therefrom into the arc passage of the insulating secondnozzlem ember r 6. The combination according to claim 5, wherein theinner surface of the annular imperforate arc shield (28) is corrugated.

7. A gas-blast circuit interrupter including a first tubular ventingcontact and a second tubular, venting contact which are cooperabletogether and relatively movable with respect to each other, anozzle-like interrupting structure comprising a first annularimperforate arc-shield (28) stationary with respect to said firstcontact and extending at least one inch along the line of relativemovement between said two venting contacts, means defining an outerannular second insulating nozzle member (34) spaced outwardly from saidinner first nozzle member and fixed with respect thereto to therebydefine an intervening substantially annular inlet passage permitting gasto flow substantially radially inwardly toward the are at a fixed level,said annular first arc shield (28) encompassing said minimum portion ofat least 1 inch of the initial arcing travel of the relatively movablefirst and second contacts, thereby forcing the drawn arc to assume aminimum length of 1 inch prior to the injection thereto of gas throughsaid inlet passage, whereby to confine the hot arc gases of theinitially-drawn portion of the established arc of at least 1 inch whilesimultaneously permitting a venting therefrom through both of saidtubular venting separable contacts, operating means to withdraw saidsecond tubular venting contact out of said first arc shield (28) therebyopening up said inlet passage, and gas-flow producing means for forcingrelatively cool gas under pressure laterally into the arc stream throughsaid annular inlet passage at said fixed level after said second tubularventing contact has withdrawn out of the first arcing shield (28), andsaid second tubular venting contact being relatively movable along saidare passage formed in said second nozzle member (34) with relativelyslight clearance so that the major proportion of the gas flow directedthrough the arc passage in the direction of relative opening movement ofsaid second tubular contact member passes interiorly of the secondtubular venting contact for venting and arc-extinguishing purposes, andrelative motion between said second tubular venting contact and saidinlet passage causing relative retracting away therefrom into the arcpassage of the insulating second nozzle member (34).

8. A gas-blast circuit interrupter including a pair of relativelymovable cooperable tubular venting contacts, at least one of which ismovable separable to establish an arc, nozzle-like interruptingstructure comprising a relatively stationary annular imperforate arcshield (28) having a length from 1 to 2 inches, at least one of saidventing contacts withdrawing from said annular imperforate arc shield28), means for establishing a radially inward-flowing gas-blast underpressure into the are following withdrawal of said one venting contactout of said annular imperforate arc shield (28) for effecting arcextinction.

9. A gas-blast circuit interrupter including a pair of relativelymovable cooperable tubular venting contacts, at least one of which ismovable separable to establish an arc, nozzle-like interruptingstructure comprising a relatively stationary annular imperforate arc 9shield (28) having a length from 1-54; inch to 1-55 inch, at least oneof said venting contacts withdrawing from said annular imperforate arcshield (28), means for establishing a radially inward flowing gas-blastunder pressure into the are following withdrawal of said one ventingcontact out of said annular imperforate arc shield (28) for effectingarc extinction.

10. The combination according to claim 8, wherein nular imperforate arcshield (28).

1. A gas-blast circuit interrupter including, in combination: a.separable cooperable tubular venting contacts at least one of which ismovable, b. nozzle-like interrupting structure comprising a relativelystationary annular imperforate arc shield (28) extending at least oneinch along the line of movement of said one movable venting contact; c.operating means operable to withdraw the movable venting contact out ofsaid imperforate arc shield (28); d. said annular arc shield (28)encompassing a minimum portion of at least one inch of the initialarcing travel of said one movable tubular venting contact, therebyforcing the drawn arc to assume a minimum length of at least one inchprior to the injection thereto of gas; and, e. fluid-flow producingmeans to inject relatively cool fluid under pressure laterally into thearc stream after said one movable venting contact has withdrawn from theimperforate arc shield (28).
 2. The gas-blast circuit interrupter ofclaim 1, wherein the inner surface of the stationary imperforate arcshield (28) is corrugated.
 3. The combination according to claim 1,wherein means defines an outer annular second insulating nozzle member(34) spaced outwardly from said inner first nozzle member to therebydefine an intervening substantially annular inlet passage permitting gasto flow radially inwardly at a fixed level at times toward the arc. 4.The gas-blast circuit interrupter of claim 1, wherein piston meansprovides the gas flow.
 5. A gas-blast circuit interrupter including apair of cooperable tubular venting contacts at least one of which ismovable, nozzle-like interrupting structure comprising a relativelystationary first annular imperforate arc shield (28) extending at leastone inch along the line of movement of the movable venting contact,means defining an outer annular second insulating nozzle member (34)spaced outwardly from said inner first nozzle member to thereby definean intervening substantially annular inlet passage permitting gas toflow radially inwardly at a fixed level at all tiMes toward the arc,said annular first arc shield (28) encompassing said minimum portion ofat least one inch of the initial arcing travel of the movable tubularventing contact, thereby forcing the drawn arc to assume a minimumlength of at least one inch prior to the injection thereto of gasthrough said inlet passage, whereby to confine the hot arc gases of theinitially-drawn portion of the established arc of at least 1 inch whilesimulataneously permitting a venting therefrom through both of saidtubular venting separable contacts, operating means to withdraw themovable tubular venting contact out of said relatively stationary firstarc shield (28) thereby opening up said inlet passage, andgas-flow-producing means for forcing relatively cool gas under pressurelaterally into the arc stream through said relatively stationary inletpassage at said fixed level after the movable tubular venting contacthas withdrawn from the first arcing shield (28) and the movable tubularventing contact movable along said arc passage formed in the secondnozzle member with relatively slight clearance so that the majorproportion of the gas flow directed through the arc passage in thedirection of opening movement of the movable contact passes interiorlyof the movable tubular venting contact for venting and arc-extinguishingpurposes, and said movable tubular venting contact pulling free of saidrelatively stationary inlet passage and retracting away therefrom intothe arc passage of the insulating second nozzle member (34).
 6. Thecombination according to claim 5, wherein the inner surface of theannular imperforate arc shield (28) is corrugated.
 7. A gas-blastcircuit interrupter including a first tubular venting contact and asecond tubular, venting contact which are cooperable together andrelatively movable with respect to each other, a nozzle-likeinterrupting structure comprising a first annular imperforate arc-shield(28) stationary with respect to said first contact and extending atleast one inch along the line of relative movement between said twoventing contacts, means defining an outer annular second insulatingnozzle member (34) spaced outwardly from said inner first nozzle memberand fixed with respect thereto to thereby define an interveningsubstantially annular inlet passage permitting gas to flow substantiallyradially inwardly toward the arc at a fixed level, said annular firstarc shield (28) encompassing said minimum portion of at least 1 inch ofthe initial arcing travel of the relatively movable first and secondcontacts, thereby forcing the drawn arc to assume a minimum length of 1inch prior to the injection thereto of gas through said inlet passage,whereby to confine the hot arc gases of the initially-drawn portion ofthe established arc of at least 1 inch while simultaneously permitting aventing therefrom through both of said tubular venting separablecontacts, operating means to withdraw said second tubular ventingcontact out of said first arc shield (28) thereby opening up said inletpassage, and gas-flow producing means for forcing relatively cool gasunder pressure laterally into the arc stream through said annular inletpassage at said fixed level after said second tubular venting contacthas withdrawn out of the first arcing shield (28), and said secondtubular venting contact being relatively movable along said arc passageformed in said second nozzle member (34) with relatively slightclearance so that the major proportion of the gas flow directed throughthe arc passage in the direction of relative opening movement of saidsecond tubular contact member passes interiorly of the second tubularventing contact for venting and arc-extinguishing purposes, and relativemotion between said second tubular venting contact and said inletpassage causing relative retracting away therefrom into the arc passageof the insulating second nozzle member (34).
 8. A gas-blast circuitinterrupter including a pair of relatively movable coopeRable tubularventing contacts, at least one of which is movable separable toestablish an arc, nozzle-like interrupting structure comprising arelatively stationary annular imperforate arc shield (28) having alength from 1 to 2 inches, at least one of said venting contactswithdrawing from said annular imperforate arc shield (28), means forestablishing a radially inward-flowing gas-blast under pressure into thearc following withdrawal of said one venting contact out of said annularimperforate arc shield (28) for effecting arc extinction.
 9. A gas-blastcircuit interrupter including a pair of relatively movable cooperabletubular venting contacts, at least one of which is movable separable toestablish an arc, nozzle-like interrupting structure comprising arelatively stationary annular imperforate arc shield (28) having alength from 1- 1/8 inch to 1- 5/8 inch, at least one of said ventingcontacts withdrawing from said annular imperforate arc shield (28),means for establishing a radially inward flowing gas-blast underpressure into the arc following withdrawal of said one venting contactout of said annular imperforate arc shield (28) for effecting arcextinction.
 10. The combination according to claim 8, wherein anadditional second insulating nozzle member (34) is provided being spacedoutwardly from said inner first nozzle member (28) to thereby define anintervening substantially annular inlet passage permitting the gas toflow radially inwardly at a fixed level toward the arc followingwithdrawal of said one contact out of the annular imperforate arc shield(28).